Polymer–Carbon Black Composite Sensors in an Electronic Nose for Air-Quality Monitoring

MRS Bulletin (Impact Factor: 5.67). 11/2004; 29(10):714-9. DOI: 10.1557/mrs2004.208
Source: PubMed


An electronic nose that uses an array of 32 polymer-carbon black composite sensors has been developed, trained, and tested. By selecting a variety of chemical functionalities in the polymers used to make sensors, it is possible to construct an array capable of identifying and quantifying a broad range of target compounds, such as alcohols and aromatics, and distinguishing isomers and enantiomers (mirror-image isomers). A model of the interaction between target molecules and the polymer-carbon black composite sensors is under development to aid in selecting the array members and to enable identification of compounds with responses not stored in the analysis library.

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    • "Nevertheless, Ryan et al. showed an increase in R/R o when PCL-carbon black composite was exposed to SO 2 , a reducing gas [47]. Carbon black is widely used as a conductive medium without specific sensing functionality and relays electrical signals detected by insulating polymers in an electronic nose [48]. In this setup, SO 2 interacts with the ester linkage , reacting with the carbonyl functional groups by donating its electron [49]. "
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    ABSTRACT: Electrospinning provides a means to synthesize nanofibrous structures with very high surface area-to-volume ratio, which enhance the sensitivity of conductive polymer (CP)-based gas sensors in a cost effective manner. To enhance processability, insulating host polymers are often used with the CP for electrospinning. Unlike CPs, however, the contribution of insulating polymers on overall sensing performance of composites has not been systemically investigated. In this study, we examined the effects of insulating polymers in electrospun composite nanofibers on the sensitivity to various analytes. Different composition ratios of polyaniline (PANI)/poly(ɛ-caprolactone) (PCL) nanofibers were produced by electrospinning, and their structure and chemistry were characterized. The PANI/PCL electrospun composite nanofibers were configured in a chemiresistor and subjected to different analytes, including H2O vapor, NH3, and NO2. H2O vapor and NO2 showed a polarity change in sensitivity, having a compositional threshold of PANI-to-PCL ratio. To investigate this polarity change, the temperature dependence of electrical conductivity was examined. When H2O vapor was exposed to the composite with the highest PANI content at 20 wt%, there was a decrease in hopping distance; on the other hand, an increase in hopping distance was observed when H2O vapor was exposed to the composite with the lowest PANI content at 9 wt%. These results show an existence of competition between the conductive polymer, PANI, and the insulating host polymer, PCL, for analyte interaction, both of which integratively determine the overall sensitivity. The work demonstrates that the host polymer plays an important role in structural swelling as well as chemical interaction with analytes, which critically modulate sensing behavior.
    Full-text · Article · Feb 2015 · Sensors and Actuators B Chemical
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    • "Hence, when a vapor is sorbed, the sensing film swells and the contact between carbon particles is broken; thereby increasing the resistance of the sensing layer. Although the resistance of the sensors is also affected by other more complex mechanisms such as sorption to carbon particles and interrupting conductive pathways or ionization of analyte in water trapped in the film, changes in the sensor resistance are indicative of changes in the vapor constituents of the environment [28] [29]. Finally, the amplitude of the signal variation and dynamics of the sensors depend on the composition of the sensing layer and the presented stimulus. "
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    ABSTRACT: A chemical detection system made of a gas sensor array and algorithms intended to monitor human activity was tested in a NASA spacecraft cabin simulator. Such a chemical-based monitoring system, if extended to home settings, would allow the autonomous detection of emergency situations, thereby postponing the moving of elderly people to assisted living facilities and improving their quality of life. Moreover, in contrast to other monitoring systems based on wearable sensors or video cameras, a monitoring system based on measuring changes in air composition induced by human activities would be non-invasive and would not raise privacy concerns when installed in homes. The third generation of the JPL sensor array was adapted in a small, compact and portable system and deployed in a spacecraft-like room for four weeks while volunteers were performing daily routines. The system was able to predict the total number of people and the level of activity performed in the room, while detecting unexpectedly high concentrations of volatiles.
    Full-text · Article · Aug 2014 · Sensors and Actuators B Chemical
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    • "For validation purposes, we refer in this letter to a comprehensive set of chemosensor recordings, the JPL data set, obtained from polymer-carbon composite sensors used in the Electronic Nose (ENose) at the Jet Propulsion Laboratory (Ryan, Zhou, et al., 2004). The JPL data set contains parallel recordings from 32 chemoresistive sensors made from insulating, commercially available polymers. "
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    ABSTRACT: The speed and accuracy of odor recognition in insects can hardly be resolved by the raw descriptors provided by olfactory receptors alone due to their slow time constant and high variability. The animal overcomes these barriers by means of the antennal lobe (AL) dynamics, which consolidates the classificatory information in receptor signal with a spatiotemporal code that is enriched in odor sensitivity, particularly in its transient. Inspired by this fact, we propose an easily implementable AL-like network and show that it significantly expedites and enhances the identification of odors from slow and noisy artificial polymer sensor responses. The device owes its efficiency to two intrinsic mechanisms: inhibition (which triggers a competition) and integration (due to the dynamical nature of the network). The former functions as a sharpening filter extracting the features of receptor signal that favor odor separation, whereas the latter implements a working memory by accumulating the extracted features in trajectories. This cooperation boosts the odor specificity during the receptor transient, which is essential for fast odor recognition.
    Full-text · Article · Dec 2008 · Neural Computation
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